Need help with unlocked Treo 180 on Cingular

I recently aquired a friends Tre 180. He tells me that it has been unlocked for all cariers, but Cingular tells me that because of this it won't function correctly. I have only been able to log onto Cingular Extend and it intermitently says bad Sim card (for a perfectly fine, tested ones), so I tend to believe them on this. If this is the case, does anyone know how to lock the phone down to just Cingular. Or, if anyone is aware of any other problem it might be, I'd be glad to hear it. I have already done the GPRS update for the phone as well.

I recently aquired a friends Tre 180. He tells me that it has been unlocked for all cariers, but Cingular tells me that because of this it won't function correctly. I have only been able to log onto Cingular Extend and it intermitently says bad Sim card (for a perfectly fine, tested ones), so I tend to believe them on this. If this is the case, does anyone know how to lock the phone down to just Cingular. Or, if anyone is aware of any other problem it might be, I'd be glad to hear it. I have already done the GPRS update for the phone as well.

I still have my T180 and have no problems using other carriers SIM card on it. I have a T-Mo phone, unlocked. Is it possible that you have a bad SIM door?